Amneal Pharmaceuticals, Inc Class A Common Stock (AMRX) had the highest return between 2008 and 2009 by a mid-cap US stock, returning 444.4%.

ASSET	YEARS	% RETURN
Amneal Pharmaceuticals, Inc Class A Common Stock (AMRX)	2008-2009	444.4%
Pegasystems (PEGA)	2008-2009	191.61%
Nova (NVMI)	2008-2009	159.44%
Eldorado Gold (EGO)	2008-2009	137.35%
Trex (TREX)	2008-2009	126.85%
NewMarket (NEU)	2008-2009	115.1%
Credit Acceptance (CACC)	2008-2009	100.76%
IAMGold (IAG)	2008-2009	93.6%
Grand Canyon Education (LOPE)	2008-2009	90.1%
Central Garden & Pet Company A (CENTA)	2008-2009	87.9%
ICL Israel Chemicals (ICL)	2008-2009	86.29%
Central Garden & Pet (CENT)	2008-2009	84.48%
Northern Oil & Gas (NOG)	2008-2009	82.15%
National Beverage (FIZZ)	2008-2009	73.25%
Galapagos NV ADR (GLPG)	2008-2009	64.07%
Buckle (BKE)	2008-2009	57.63%
Hawkins (HWKN)	2008-2009	55.5%
LivaNova (LIVN)	2008-2009	55.32%
First Financial Bankshares (FFIN)	2008-2009	52.26%
Companhia Paranaense de Energia Pref ADR (ELP)	2008-2009	52.2%
Balchem (BCPC)	2008-2009	51.4%
FirstCash (FCFS)	2008-2009	51.16%
Skechers (SKX)	2008-2009	50.66%
American Superconductor (AMSC)	2008-2009	48.94%
Sandstorm Gold Ltd N (SAND)	2008-2009	48.7%

Mid-cap stocks are treated as having a market cap between $2B and $10B.